Re: [Qemu-ppc] [Qemu-devel] [PATCH v2 13/18] hw/nvram/fw_cfg: Add QMP 'info fw_cfg' command

[Markus Armbruster]

The subject "Add QMP 'info fw_cfg' command" misspells query-fw_cfg-items
:)

Eric Blake <address@hidden> writes:

> On 3/7/19 7:32 PM, Philippe Mathieu-Daudé wrote:
>> When debugging a paravirtualized guest firmware, it results very
>> useful to dump the fw_cfg table.
>> Add a QMP command which returns the most useful fields.
>> Since the QMP protocol is not designed for passing stream data,
>> we don't display a fw_cfg item data, only it's size:
>> 
>> { "execute": "query-fw_cfg-items" }
>> {
>>     "return": [
>>         {
>>             "architecture_specific": false,
>>             "key": 0,
>>             "writeable": false,
>>             "size": 4,
>>             "keyname": "signature"
>
> You could return a base64-encoded representation of the field (we do
> that in other interfaces where raw binary can't be passed reliably over
> JSON).  For 4 bytes, that makes sense,
>
>
>>         {
>>             "architecture_specific": true,
>>             "key": 3,
>>             "writeable": false,
>>             "size": 324,
>>             "keyname": "e820_tables"
>
> for 324 bytes, it gets a bit long. Still, may be worth it for the added
> debug visibility.
>
>
>> +++ b/qapi/misc.json
>> @@ -3051,3 +3051,47 @@
>>    'data': 'NumaOptions',
>>    'allow-preconfig': true
>>  }
>> +
>> +##
>> +# @FirmwareConfigurationItem:
>> +#
>> +# Firmware Configuration (fw_cfg) item.
>> +#
>> +# @key: The uint16 selector key.
>> +# @keyname: The stringified name if the selector refers to a well-known
>> +#           numerically defined item.

Ignorant questions, I'm afraid...

What determines the possible values of @key?

What's the difference between a "well-known" and a "not well-known"
value?  Examples?

>> +# @architecture_specific: Indicates whether the configuration setting is
>
> Prefer '-' over '_' in new interfaces.
>
>> +#                         architecture specific.
>> +#                  false: The item is a generic configuration item.
>> +#                  true:  The item is specific to a particular architecture.
>> +# @writeable: Indicates whether the configuration setting is writeable by
>> +#             the guest.
>
> writable
>
>> +# @size: The length of @data associated with the item.
>> +# @data: A string representating the firmware configuration data.
>
> representing
>
>> +#        Note: This field is currently not used.
>
> Either drop the field until it has a use, or let it be the base64
> encoding and use it now.
>
>> +# @path: If the key is a 'file', the named file path.
>> +# @order: If the key is a 'file', the named file order.
>> +#
>> +# Since 4.0
>> +##
>> +{ 'struct': 'FirmwareConfigurationItem',
>> +  'data': { 'key': 'uint16',
>> +            '*keyname': 'str',
>> +            'architecture_specific': 'bool',
>> +            'writeable': 'bool',
>> +            '*data': 'str',
>> +            'size': 'int',
>> +            '*path': 'str',
>> +            '*order': 'int' } }
>
> Is it worth making 'keyname' an enum type, and turning this into a flat
> union where 'path' and 'order' appear on the branch associated with
> 'file', and where all other well-known keynames have smaller branches?

Discriminator can't be optional.  Obvious solution: add a suitabable
enum value for "other" key values.

Leads to something like this (untested):

    { 'union': 'FirmwareConfigurationItem',
      'base': { 'key': 'uint16',
                'keyname': 'FirmwareConfigurationKey',
                ... more members that make sense regardless of @key ... },
      'discriminator': 'key',
      'data': {
                'file': 'FirmwareConfigurationItemFile',
                ... more variants, if any ... } }

where 'FirmwareConfigurationItemFile' is a struct type containing the
members that make sense just for 'file'.

>> +
>> +
>> +##
>> +# @query-fw_cfg-items:
>
> That looks weird to mix - and _. Any reason we can't just go with
> query-firmware-config?
>
>> +#
>> +# Returns the list of Firmware Configuration items.
>> +#
>> +# Returns: A list of @FirmwareConfigurationItem for each entry.
>> +#
>> +# Since 4.0
>> +##
>> +{ 'command': 'query-fw_cfg-items', 'returns': ['FirmwareConfigurationItem']}
>>